(1) Field of the Invention
The present invention belongs to the technical field of video output technology.
(2) Related Art
A video output technology concerns playing back video signals recorded on recording media or transmitted via a transmission line, and outputting video signals that conform to the scanning system designated by the mode set in playback devices.
Conventionally, these video signals had been output at 60 fps (or 60/1.001 fps) so as to enable playback on a television receiver. However, following the popularization of monitors, projectors, computer monitors, and the like that are compatible with 24 fps (or 24/1.001 fps) capable of using frame rate for movies without conversion, the new trend in recent years has been to output video signals for movies at 24 fps frame rate.
The output frame rate of video signals in a playback device depends on the status settings of the device. The status setting are set to default values when the device is shipped by manufactures, with users being able to freely change these settings via a graphic user interface (GUI) menu or the like.
For example, according to an art disclosed in the Patent Document 1, a BD player outputs video by switching a frame rate of video signals between 60 fps and 24 fps depending on an original frame rate of the video signals to be played back, only after a user has intentionally set the operation mode of the playback device to the discontinuous mode that permits switching of frame rate during playback.
Suppose a case where a playback device is connected with a display device via a connection such as the High Definition Multimedia Interface (HDMI) standards in which data is transmitted between these devices in synchronization with each other. If a frame rate is switched during playback, re-synchronization between the playback device and the display device needs to be performed. Output of video will be suspended during the re-synchronization. However, according to the playback device disclosed in the Patent Document 1, the user is only permitted to select the discontinuous mode after being informed of the possibility of interrupted playback during output of mixed signals of 60 Hz and 24 Hz signals. Accordingly, product complaints are unlikely to arise even if re-synchronization causes image disruption during playback.
Patent Document 1: Japanese Laid-Open Patent Application Publication No. 2006-222938 (FIG. 1)
Non-Patent Document 1: Hi-Vi Magazine, September 2007 Issue, pp. 118-123 (Stereo Sound Publishing, Inc.)
By the way, the BD-ROM standards stipulate that a fixed frame rate of video data constituting one playlist should be used. Accordingly, even if the discontinuous mode has been set in the BD player disclosed in the Patent Document 1, re-synchronization due to switching of the frame rate does not cause intermittent images during playback of one playlist of the main feature.
Compared with this, since the DVD-Video standards do not stipulate that a fixed frame rate of video data constituting one playlist should be used, one playlist might include both 24 Hz signals and 60 Hz signals. In particular, there has recently been a demand for improving image quality of DVD-Videos by recording video signals at 24 fps that is the same as the frame rate of movie materials, without conversion. This results in a high possibility of supply of the main feature composed of one playlist in which signals have different frame rates.
If the art disclosed in the Patent Document 1 is applied to a DVD player in such a situation, a frame rate of video signals is likely to be frequently switched even during playback of one playlist constituting the main feature. As a result, occurrence of intermittent images might dramatically increase. Since understanding of such a case is difficult for beginner users having less technical knowledge, it is concerned that new type product complaints might arise.